Stackable chair



FIG. 1 is a top, front, right-side perspective view of a stackable chair showing my new design;

FIG. 2 is a left side-elevational view thereof, the right side being mirror symmetrical thereto;

FIG. 3 is a front view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a rear view thereof; and,

FIG. 6 is a bottom view thereof. 

The ornamental design for a stackable chair, as shown and described. 